There has been a recent increase in demand for wireless sensor networks, due to their simplicity, low cost and easy deployment. Wireless sensor networks can serve different purposes, from measurement and detection, to automation and process control.
A typical wireless sensor network consists of sensor nodes (SNs) and sinks. SNs are wireless nodes equipped with sensing devices whose goal is to gather data in the environment and transmit it to a central server. It is advantageous if the transmission is wireless, since the number of sensors is typically very large, and the cost of deployment of a wired infrastructure would be more expensive.
In order to have a longer lifetime, SNs typically use smaller transmission powers. The area covered by a sensor network may be large enough that intermediate devices are useful to relay data. These devices are data sinks and are called cluster heads (CHs). A CH is a device whose task is to capture transmissions of SNs in its environment, optionally do some limited processing of the data, and to forward the data to a central server. One CH is responsible for coordinating a number of SNs: for a network of 100 SNs, there may be less than 10 CHs, depending on the network area.
Since there are much fewer CHs than SNs, they can be more expensive. They can rely on more sophisticated wireless technology to transmit data to the central server, or in some cases they can also be wired.
In many applications of sensor networks, a network is desired to cope with bursts of high data rates. One example is an intrusion detection network, where once an intruder is detected, a number of sensors, including video cameras, are activated to inform about the intrusion. A similar example is a fire detection problem. In these applications it is seen that, even though the average packet rates are relatively low e.g. since intrusion or fire events are typically rare events, a network is desired to be able to support higher rate bursts.